Reversing a vehicle while towing a trailer may be difficult. One reason for such difficulty is that backing-up a vehicle with an attached trailer requires steering inputs that are opposite to normal steering when backing-up the vehicle without a trailer attached and/or requires braking to stabilize the vehicle-trailer combination before a jackknife condition occurs. Another reason for such difficulty is that small errors in steering while backing-up a vehicle with an attached trailer are amplified thereby causing the trailer to depart from a desired path.
Known trailer backup assist systems may assume that a driver of a vehicle with an attached trailer wants to backup straight and the system either implicitly or explicitly assumes a zero curvature path for the vehicle-trailer combination. Most real-world situations involve a curved trailer path. Thus, assuming a path of zero curvature may significantly limit the usefulness of the system.
Some known systems assume that a path is known from a map or path planner. To this end, some known trailer backup assist systems operate under a requirement that a trailer backup path is known before backing-up of the trailer commences such as, for example, from a map or a path-planning algorithm. Such systems may have a relatively complex human machine interface (HMI) device to specify the path, obstacles and/or goal of the backup maneuver.
Another reason backing-up a trailer can prove to be difficult is the need to control the vehicle in a manner that limits the potential for a jackknife condition to occur. Typically, a jackknife condition exists when the hitch angle cannot be reduced (i.e., made less acute) while continuously backing-up a trailer by application of a maximum steering input for the vehicle. If the jackknife angle has been reached or exceeded, the vehicle must be pulled forward to reduce the hitch angle in order to eliminate the jackknife condition and, thus, allow the hitch angle to be controlled via manipulation of the steered wheels of the vehicle. The jackknife condition can also lead to damage to the vehicle and/or trailer if certain operating conditions of the vehicle relating to its speed, engine torque, acceleration, and the like are not detected and counteracted. For example, if the vehicle is travelling at a sufficiently high speed in reverse and/or subjected to a sufficiently high longitudinal acceleration when the jackknife condition is achieved, the relative movement of the vehicle with respect to the trailer can lead to contact between the vehicle and trailer thereby damaging the trailer and/or the vehicle.